It is emphasized here that the invention relates more specifically to rotating machines for manufacturing containers from thermoplastic material, particularly PET, by blow-molding or stretch-blowing a preform (intermediate container) in molds supported on a rotating frame, but the invention can be applied to other types of rotating machines such as filling machines.
FIG. 1 of the attached drawings shows a side view of a rotating electricity and fluid supply column installed at present in some machines for manufacturing containers by blow-molding or stretch-blowing, produced by the applicant (the principal parts of a machine of this type are sketched in a highly schematic way in FIG. 1).
The rotating machine of the carousel type comprises a fixed frame 1 supporting a rotating frame 2 which is rotatable (by the action of means which are not shown) about an axis 3 of rotation. The rotating frame 2 supports a plurality of workstations 4 distributed regularly around the periphery. More specifically, in the example considered here of a stretch-blowing machine for manufacturing containers, particularly bottles from thermoplastic material such as PET, each workstation 4 comprises, in particular, a mold 5, means 6 for controlling the preblowing fluid under relatively medium pressure (typically about 13×105 Pa) and the blowing fluid under relatively high pressure (typically about 40×105 Pa) and a rod 7 for mechanically stretching the container during the blowing, the rod 7 being moved axially by pneumatic actuating means 8 (of the air cylinder type) under relatively low pressure (typically 7×105 Pa).
The machine also has a rotating electricity and fluid supply column 9 which extends coaxially with the axis 3 of rotation of the rotating frame, and which can supply the electricity and the various fluids required for the operation of the workstations 4 from respective fixed sources.
For this purpose, the rotating column 9 comprises a rotating electric collector 10, located at the top of the rotating column 9, which is supplied by a fixed electrical cable 11. In a conventional way, the rotating electric collector has fixed or rotating tracks on which rotating or fixed brushes, respectively, bear resiliently, the assembly being protected by a casing 12, shown in FIG. 1 only, which is fixed and retained by an anti-torque structure 13 (shown schematically in the form of a bracket) fixed to the fixed frame 1.
Below the rotating electric collector 10 there is an axially positioned rotating fluid connection 14, of which only the casing 15, fixed and retained by the anti-torque structure 13, is shown in FIG. 1. The rotating fluid connection 14 is connected to a source of pneumatic fluid under relatively high pressure (generally air at about 40×105 Pa) by a pipe 16 and to a source of pneumatic fluid under relatively low pressure (in practice, air at the industrial pressure of 7×105 Pa) by a pipe 17, the two pipes 16 and 17 being fixed and supported, for example, by the anti-torque structure 13.
The base 18 of the rotating supply column 9, with which it rests on the fixed frame 1, is also fixed. The rotating part, or rotor, of the rotating column 9 is indicated as a whole by the reference 19 in FIG. 1.
The supplies are provided to the workstations in the following manner.
The electrical output cables of the rotating electric collector 10, which are indicated by the reference 20, are fixed to the rotor 19 of the rotating column 9 and, in order to keep them disengaged from the anti-torque structure 13, are made to pass through the rotating fluid connection 14 while being functionally associated with the rotor 19, after which, at the outlet of the rotating fluid connection 14, they are connected to an electrical distribution box 21 supported by the rotating frame used for supplying electricity to the electrical components of workstations (solenoid valves, for example).
The pneumatic fluid is taken from the outlet of the rotating fluid connection 14 through the rotor 19 which is of hollow construction (an example of the structure of the rotating fluid connection 14 is described below with reference to FIGS. 2A and 2B), toward a rotating fluid distributor 22 located under the rotating fluid connection 14. The distributor 22 has a first stage consisting of connections 23, distributed peripherally for the distribution of the pneumatic fluid under low pressure and connected at 24 to the means 8 for actuating the stretching rod 7. The distributor 22 also has a second stage consisting of connections 25 distributed peripherally for the distribution of the pneumatic fluid under high pressure (blowing) and connected at 26 to the aforesaid means 6 for controlling the preblowing and/or blowing fluid. Finally, the distributor 22 also has a third stage consisting of connections 27 distributed peripherally for the distribution of the pneumatic fluid under medium pressure (preblowing) and connected at 28 to the aforesaid means 6 for controlling the preblowing and/or blowing fluid; the fluid under medium pressure (typically 13×105 Pa) is normally obtained by drawing fluid under high pressure at 29 from the corresponding stage of the distributor, this fluid being expanded in a pressure reducer 30 to bring it to the requisite pressure and finally being stored in a buffer reservoir 31 (for example, one incorporated in a structure 66 of the rotor 19 as shown in FIG. 1) which is connected to the aforesaid third stage of connections 27.
Finally, below the buffer reservoir 31, the rotor has a liquid distributor 32 which is designed for distributing the requisite water and oil at 33 and 34 to each workstation, for regulating the temperature of the molds 5 for example.
An assembly flange 63 is provided at the base of the distributor 22 to enable it to be fixed removably to the underlying part 66 of the rotor 19.
In FIGS. 2A and 2B of the attached drawings, the rotating fluid connection 14 is shown in diametric sections taken along two respective perpendicular planes. The fixed outer part or casing 15 is provided with a first radial bore 35, for the admission of fluid under high pressure (arriving from the pipe 16), which opens into a first annular distribution chamber 36, and with a radial opening 37 formed by a second bore, located below the first bore, for the admission of fluid under low pressure (arriving from the pipe 17), which opens into a second annular distribution chamber 38.
Inside the casing 15, the rotating part 39 of the rotating fluid connection 14 (which forms one of the elements of the rotor 19 of the rotating column 9) has a first radial bore 40 facing the first annular distribution chamber 36 of the casing 15 and an axial bore 41 opening into this first radial bore 40 and extending downward toward the underlying rotating fluid distributor 22 (shown in FIG. 1). The rotating part 39 has a second radial bore 42 facing the second annular distribution chamber 38, the said second radial bore 42 opening into the axial bore 41. Finally, a central tube 43 is mounted in the axial bore 41, coaxially with the latter; the central tube 43 has a smaller outside diameter than that of the axial bore 41, in such a way that an annular passage 44 is formed between the central tube 43 and the axial bore 41; additionally, the upper end of the central tube 43 is fixed in a sealed way to the axial bore 41 in the part of the latter located between the two radial bores 40 and 42.
Because of this arrangement, the central tube 43 carries in an axial direction the pneumatic fluid under high pressure delivered by the pipe 16 via the first annular distribution chamber 36 and the first radial bore 40, while the annular passage 44 carries in a peripheral direction the pneumatic fluid under low pressure delivered by the pipe 17 via the second chamber 38 and the second radial bore 42.
As shown in FIG. 2B, drawn in a perpendicular section plane, the rotating part 39 of the rotating fluid connection 14 is also provided with a bore 45 parallel to its axis and to the axial bore 41, but offset radially toward the periphery of the rotating part 39, in such a way that it passes outside the axial bore 41, extending over approximately the whole height of the rotating part 39. The off-centered bore 45 is intended for the passage of the electrical cable or cables 20 which extend from the outlet of the rotating electric collector 10 to the electrical distribution box 21, as mentioned above.
In some cases, the structure is provided with a plurality of bores among which the cables are distributed, instead of being provided with a single off-centered bore 45 for the passage of the cables.
A rotating electricity and fluid supply column 9 designed as described above is currently fitted to many machines manufactured by the applicant, and has proved entirely satisfactory in respect of its function. However, this known column has a number of drawbacks due to its structure, and more specifically due to the relative positions of the rotating electric collector 10 and the rotating fluid connection 14.
Because of the position of the rotating fluid connection 14 located below the rotating electric collector 10, any servicing work carried out on the rotating fluid connection 14 requires the dismantling of the rotating electric collector 10, with all the operations necessitated by this (electrical isolation of the machine, disconnection of the cables, separation of the anti-torque structure, check of the correctness of the connections after reassembly, etc.). In current practice it has been found that servicing is performed relatively rarely on the rotating electric collector 10, whereas the rotating fluid connection requires regular servicing.
One important reason for the servicing work is the need for regular replacement of the seals 46 between the fixed part and the rotating part, which have a relatively short lifespan. Owing to the presence of the off-centered bore or bores 45, the rotating part 39 of the rotating fluid connection has been designed with a relatively large diameter (typically from 110 to 150 mm in the applicant's machines). Consequently, the linear velocity of the rotating part relative to the fixed part is high. Because of this, the seals undergo accelerated mechanical wear.
Furthermore, this high relative velocity causes a relatively intense heating of the seals (whose temperature can be raised to about 100° C., for example). This heating is communicated to the metal parts and particularly to the rotor, which, for reasons described above, is massive and therefore difficult to cool. This unfavorable thermal environment considerably affects the lifespan of the seals.
Moreover, the seals 46 are housed in grooves machined in the wall of the casing 15 (closed groove fitting). Since the seals 46 are made from a relatively rigid material, they must be deformed to their cores in order to fit them, so that they can be inserted into the casing until they reach their respective grooves in which they are subsequently expanded. However, the constituent material of the seals is not resilient, and, when inserted into their grooves, the seals do not easily return to their annular shape, and therefore manual intervention is required in order to shape them correctly.
Consequently, users urgently require improvements to this part of the machine, in order to simplify maintenance and increase the time between services, so that the machines can become more efficient and productive.